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Message:: [QUOTE="uncleal13, post: 12231679, member: 28026"]I had a 2013 4900SF, first two winters here in Saskatchewan cab was cold, side windows would frost up going down the highway, would only clear when stopped. Third winter I unhooked the cab heater hose off the heater control valve to flush out the heater core.I happened to glance at the port of the valve and saw that it was mostly closed, only open about 1/8”. I knew my cab setting was full heat. I double checked and confirmed it was selected hot. I got looking at the valve. The arm were the control cable was attached was mounted into a hole that was too far from  the body of the valve so it had lots of leverage but didn’t rotate the valve very far. I drilled a hole into the arm about half way down and installed the cable. It was now harder to turn the control knob, but the valve now would rotate fully open. After that the cab was roasting hot, and the windows stayed clear.[/QUOTE]